Halogenated hydrocarbons such as, e.g., chlorocarbons, are a major source of environmental pollution and toxic waste. These hydrocarbons are the products or by-products of several industrial processes and present serious health hazards. Accordingly, they must either be destroyed or converted to passive, non-toxic products.
One method of destruction of such toxic materials involves their thermal destruction, which requires a temperature above 1000.degree. C. However, even at such high temperatures some toxic materials such as polychlorinated biphenyls (PCBs) survive or they are converted to the more toxic polychlorinated dibenzo-p-dioxins (PCDD). Moreover, toxic nitrous oxides (N.sub.2 O) are also formed at these temperatures.
Other methods of destruction of halogenated hydrocarbons have been disclosed in the prior art. For example, multi-stage catalytic destruction of PCBs is disclosed by Lombardi et al, "Incineration of PCBs Using Fluidized Bed Incinerator," Rockwell International: Golden, CO, 1981. However, this method involves multi-stage operation for high conversion, is complicated, costly and inefficient.
Others have used catalysts on monolithic supports to oxidize the halogenated hydrocarbons. See P. Subbanna et al, Environmental Science Technology, 1988, Vol. 22, pp. 557-561. Although this method has the advantage of a low pressure drop operation, it results in low conversion of the toxic hydrocarbons and the generation of many secondary toxic products. Moreover, in order to improve the conversion of the toxic hydrocarbons, this catalytic process, as in the aforementioned Lombardi et al article, requires multi-stage operation and a temperature of 600.degree. C. or higher at which both nitrous oxide and highly refractory toxic materials are formed.
Other methods of destruction of toxic wastes involve chemical treatment with sodium or calcium. See Chemical Engineering, 1981, Vol. 88(16), pp.37-41. However, these methods involve the use of dangerous chemicals, are highly exothermic and have not been practical industrially.
Photochemical, biological and hydrogenation methods of conversion of halogenated hydrocarbons have also been resorted to, but they require complex technology and dangerous operations. Besides, they are economically prohibitive.
See, also, Michael P. Manning, "Fluid Bed Catalytic Oxidation: An Underdeveloped Hazardous Waste Disposal Technology," Hazardous Waste, Vol. 1, No. 1, 1984, pp.41-65; James K. Musick et al, "Hopcalite Catalyst for Catalytic Oxidation of Gases and Aerosols," Ind. Eng. Chem., Prod. Res. Dev., Vol.14, No.4, 1975, pp.284-286, and K. P. Becker et al, "Incinerate Refinery Waste in a Fluid Bed," Hydrocarbon Processing, October 1975, pp. 88-93.
Several prior art patents also disclose the destruction of hazardous wastes. Most of these patents are directed to halogenated hydrocarbons, principally chlorinated hydrocarbons, since they cause the most difficulties in the destruction process. Exemplary patents include U.S. Pat. Nos. 3,845,191; 4,039,623, and 4,447,667.
U.S. Pat. No. 3,845,191 discloses a process for the purification of waste streams containing halocarbons which comprises oxidation of the halocarbons at a temperature of 750.degree. C. to 1100.degree. C. with a metal oxide catalyst selected from the group consisting of an oxide of calcium, aluminum, barium, magnesium, iron or nickel.
U.S. Pat. No. 4,039,623 describes a method of treating C.sub.2 to C.sub.4 halogenated hydrocarbons such as chlorinated hydrocarbons and brominated hydrocarbons whereby the halogenated hydrocarbons in a gas stream are oxidized with an oxygen-containing gas in the presence of hydrated nickel oxide catalyst at a temperature of 20.degree. C. to 500.degree. C. This process reduces the halogenated hydrocarbon content of the gas stream.
U.S. Pat. No. 4,447,667 discloses a process for the destruction of halogenated organic compounds by reaction with an alkali metal aromatic anion reagent such as sodium naphthalide.
So far as it is known, there is presently no simple, efficient and economical method for the destruction of such toxic halocarbons and their conversion into non-toxic products. Needless to say, there is now a dire need for such method in order to reduce the amount of toxic waste materials associated with halogenated hydrocarbons.
Accordingly, it is an object of this invention to provide a method for the destruction of toxic organic chemicals.
It is a further object of this invention to convert toxic halocarbons or toxic halocarbons-containing waste materials into non-toxic products.
It is another object of this invention to provide an efficient catalytic method of converting toxic halocarbons such as, e.g., chlorocarbons, to non-toxic by-products.
It is still another object of this invention to provide a catalytic method of destruction of chlorocarbons by contacting the chlorocarbon with an oxygen-containing gas in the presence of a unique catalyst system which comprises a metal or metal oxide in the presence of alkali or alkali-earth carbonate, or alkali earth oxide and hydroxide.
The foregoing and other objects and features of this invention will be more readily understood from its following detailed description.